This lets you customize which font to use for the various text elements on the RRD graphs. DEFAULT sets the default value for all elements, TITLE for the title, AXIS for the axis labels, UNIT for the vertical unit label, LEGEND for the graph legend, WATERMARK for the watermark on the edge of the graph.

Use Times for the title: --font TITLE:13:Times

Note that you need to quote the argument to --font if the font-name contains whitespace: --font "TITLE:13:Some Font"

If you do not give a font string you can modify just the size of the default font: --font TITLE:13:.